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ANP PROJECT PROGRESS REPORT
TABLE 2.2.4. DATA FOR THE REACTION OF UF,
WITH IRON IN LIF-ZrF, (52-48 MOLE %) AND IN
KF-ZrF, (52-48 MOLE %) AT 600 AND 8OO0C
Conditions of
Equilibration
Present in Filtrate
~ ~~
Temperature Time Total U Total Fe* Total Ni
(O c) (hr) (wt 96) ( P P ~ (PPd
Solvent: LiF-ZrF4 (52-48 mole %)
600 3 9.1 460
3 10.0 550
5 9.7 460
5 9.9 520
800 3 9.8 360
3 9.6 390
5 9.6 400
5 9.5 350
Solvent: KF-ZrF, (52-48 mole %)
600 3 7.2 520
3 8.0 630
5 7.7 490
5 7.9 510
800 3 8.2 330
3 8.1 280
5 8.1 310
5 8.1 330
30
35
40
65
15
20
35
35
1
10
5
10
65
30
70
35
*Blanks of 100 and 40ppm of Fe at 8WoC for LiF-Zr F,
and KF-ZrF,, respectively,
The indifference exhibited by the UF Feo reaction
4:
to changes in the reaction medium IS in marked
contrast to the behovior noted for the UF,-Cr r e
action. No satisfactory explanation can be offered
at this time for these differences.
SOME OBSERVATIONS ON MASS TRANSFER
OF CHROMIUM BY MOLTEN SALTS
W. R. Grimes
When the corrosion of lnconel by NaF-ZrF,-UF,
mixtures and by NaF-KF-LiF-UF, mixtures is
compared, some striking differences are observed.
The corrosion, as measured by depth of void forma-
96
tion in the hot region of a system with a temperature
gradient, is much worse when the circulated fluid
is the alkali fluoride mixture than when it is the
ZrF,-bearing fuel. In addition, discrete crystals
of nearly pure chromium are found in the cold
zones of lnconel loops in which the NaF-KF-LiF-
UF, mixture has been circulated. Metallic deposits
are not usually observed in loops which have cir-
culated the NaF-ZrF4-UF, preparations. Depth of
void formation does increase with time, however,
for both classes of systems, even though the con-
centration of chromium compounds in solution
reaches an equilibrium concentration early in the
corrosion test and remains essentially constant
thereafter. The amount of chromium removed from
the loop walls, as estimated from the volume of
voids in the hot zone, is considerably larger than
can be explained by the amount of chromium com-
pound in solution in the melt after the test. More-
over, the corrosion seems to be nearly independent
of the ratio of the-surface area of the loop to the
volume of the melt and not strongly dependent on
the concentration of uranium in the melt.
The processes that occur are undoubtedly very
complex, and it is not possible to explain in
quantitative fashion all the effects observed.
However, by the use of equilibrium data obtained
for the chemical reactions and by making some
reasonable assumptions it is possible to rationalize
much of the available data and to indicate a pos-
sible explanation for the observed similarities and
differences in these two fuel classes. For ZrF,-
bearing mixtures, of which the mixture with 50 mole
75 NaF, 46 mole 75 ZrF,, and 4 mole 75 UF, is
typical, the important corrosion reaction is known
to be
Na F-ZrF4
2UF4 + Cr CrF, + 2UF,
The equilibrium constant for this reaction is given
by
where the quantities in parentheses represent the
activities of the materials involved. The equi-
librium constant, K;,,, cannot be determined by
experiment, but the equi I i brium concentration,
u
i
.
*